This invention relates to coated, molded articles. In one aspect, this invention relates to coated, molded articles comprising a plastic laminated to an abrasion resistant coating while in another aspect, this invention relates to a dual cure, in-mold process for making these articles. In yet another aspect, this invention relates to molded, plastic articles coated with a composition comprising poly- and monofunctional acrylic monomers, acrylic-soluble thermoplastics having hydroxy functionality, and an aminoplast resin.
Molded thermoplastic articles, such as those made from polymethylmethacrylate, polycarbonate, polyester carbonates, polyester and polystryrene, are commonly used in a wide variety of applications including automotive head and tail lamps, glazing, optical lenses, aircraft parts, signs, display and store fixtures and furniture, to name but a few. Since the surfaces of these thermoplastics are quite soft and are easily scratched and marred during normal use, these surfaces are commonly treated with an abrasion resistant coating.
Many coatings have been proposed for post-application onto the finished molded articles. These materials are applied by conventional coating methods such as spraying, dipping, brushing and roll coating. One common type of a post-application coating is the solvent-based, thermally crosslinkable type, such as the polysiloxanes, fluorocarbonvinyl ether copolymers, and polyurethanes. These materials, when cured, offer various degrees of abrasion resistance, gloss, weatherability, chemical resistance, and adhesion to the thermoplastic substrate. However, these materials suffer certain disadvantages, some serious, such as slow cure, high energy requirements to convert and/or eliminate solvent, emission of enviroment damaging solvents, and cosmetically undesirable features, e.g. orange peel, craters, fish eyes and the presence of airborne dust particles.
Another type of post-application coating is the 100% solids, UV radiation-curable coating type. These materials overcome some of the disadvantages associated with the solvent-based materials, such as high energy consumption and solvent emissions but because of their higher viscosities, they suffer even more from the previously described surface defects as well as poor adhesion to some thermoplastic compositions. These materials also have a tendency to stress crack when applied at higher film thickness. The addition of nonreactive thermoplastic polymers or monofunctional monomers can reduce or eliminate cracking, but only with a diminished resistance to abrasion, chemicals and weathering. In addition, the cure of these coatings by UV radiation is inhibited by atmospheric oxygen, and this results in lower molecular weight polymers at the surface and thus a coating with less hardness, abrasion resistance, chemical resistance, gloss and weatherability than would otherwise be the case. This inhibition can be overcome by conducting the cure in an inert atmosphere, but this is comparatively costly and impractical when the article is large and of a complex shape.